X-ray system



May 5, 1959 G. DEs'rRlAu 2,885,558

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United States. Patent 'O X-RAY SYSTEM Georges Destriau, Cauderan, France, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 13, 1957, Serial No. 645,694 9 claims. (c1. 25o-71) This invention relates to X-ray-electroluminescent devices and, more particularly, to a method for storing and later releasing an X-ray image, which released image may have an enhanced output.

It is desired for many purposes to be able to store or commit to memory a uoroscopic image corresponding to an X-ray signal and to release this stored image at a later time. In addition, it is desirable to use a smaller X-ray intensity in order to achieve the brightestpossible image on a fluoroscopic screen, since the deleterious effects of X-rays on living organisms is well known. It is the general object of this invention to avoid and overcome the foregoing and other diiculties of and objections to the prior art practices by the provision of a method for storing and later releasing the luminous response to an X-ray signal of an X-ray-responsive phosphor screen.

It is a further object to provide a process for storing and later releasing with enhanced output the luminous response to an X-ray signal of an X-ray-responsive phosphor screen.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by providing a process for operating an X-ray system incorporating an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when excited by X-rays and simultaneously placed within the influence of van alternating electric field. In the operation of this system, the phosphor screen is presensitized by applying thereto the X-ray signal which is to be stored or memorized and simultaneously applying across the screen an alternating electric field. This so-called presensitizing X-ray signal-screen irradiation is then stopped and the screen is removed from the influence of the alternating electric field. The phosphor screen excitation takes the form of an image of the object being X-rayed and corresponds to the X-ray signal impressed on the screen. This image is stored in the screen by this procedure and the phosphor screen is thus presensitized To release this stored image, the presensitized screen is thereafter irradiated with X-rays, which cause the presensitized screen to release the stored image, with enhanced output in some cases as specified hereafter. In addition, there has been provided an apparatus for accomplishing this image storage or image storage and intensification.

For a better understanding of the invention, reference should be had to the accompanying drawings, wherein:

Fig. 1 is a sectional elevation of the preferred X-rayelectroluminescent fluoroscopic screen;

Fig. 2 is a schematic diagram of the X-ray unit and operating circuit therefor illustrating the phosphor screenpresensitizing operation wherein the X-ray image is stored in the fluoroscopic screen;

Fig. 3 is a schematic diagram similar to Fig. 2 illustrating the second phase of the equipment operation, wherein the .stored image is released from the tiuoroscopic screen;

2,885,558 ce Patel-.mamey 5,1959

Fig. 4 is a graph of brightness in arbitrary units vs. time in minutes illustrating thefsignal-storage capabilities of the fiuoroscopic system;

Fig. 5 is a graph of brightness in arbitrary units vs. time in minutes illustrating the storageand brightnessenhancement capabilities of the fluoroscopic system;

Fig. 6 is a graph of the ratio of enhanced output vs. time of rest (in minutes) showing the effect on releasedimage brightness when increasing the storage period for the stored image.

Although the principles of the invention are broadly applicable to any system wherein an X-ray-responsive phosphor of the type specified herein is to be irradiated by X-rays, the invention has particular reference to fluoroscopic screens which are fabricated similar to an electroluminescent cell and hence it has been so illustrated and will be so described.

In copending application of G. Destriau, the inventor herein, S.N. 433,185, filed May 28, 1954, titled X-ray Electroluminescent Screen and assigned to the present assignee, is disclosed an X-ray-electroluminescent device wherein the output of an X-ray-responsive phosphor is enhanced by the simultaneous application of an electric field across the phosphor. This enhanced output enables a smaller dosage of X-rays to be used in order to achieve a usable brightness of the fluoroscopic screen or, alternatively, makes possible a brighter picture without increasing the dosage of X-rays. As disclosed in this copending application, the phosphor materials which may be used will display an enhanced lumino-us output when excited by Xfrays and simultaneously placed within the influence of an alternating electric field. This is contrary to the action of most phosphors which will display a quenching effect under similar conditions. The `phosphors which may be used in the instant system are those which may be used in the so-called X-ray-enhancement as disclosed in the heretofore-mentioned copending Destriau application, namely those phosphors which display an enhanced output when irradiated with X-rays and simultaneously placed within the influence of an alternating electric field. Specific phosphors which will be suitable for the instant purpose are mixtures vof zinc sulfide and cadmium sulfide wherein the molar ratio of zinc to cadmium is from nine mole parts zinc, one mole part cadmium to three mole parts zinc, seven mole parts cadmium and activated by from 0.01 10*2 to 6.0 102 mole of manganese per mole of luminescent material. In addition, the phosphor material may be activated by a mixture of manganese and silver, with the silver being present in amounts of from traces (0.001 to 10-2 mole silver per mole manganese) up to about 1.0 l0-2 mole silver per mole manganese. Also, zinc sulfide phosphors which are activated with manganese or mixtures of manganese and silver in the heretofore-disclosed amounts are also suitable. As a specific example, the phosphor material may comprise 1CdS3.5ZnS, activated by 1x10-4 mole manganese per mole of luminescent material, such a phosphor having been fired during preparation at a temperature of from 800 C. to 1150 C.

In Fig. l is illustrated the preferred embodiment of the electroluminescent-uoro-scopic screen 10 which comprises a substantially planar layer of luminescent material 12 adjacent a substantially planar layer of dielectric material 14 with the luminescent and dielectric materials being sandwiched between two thin, conductinglayers or electrodes 16 and 18. Each of the electrode layers 16 and 18 may be connected through suitable busv hars 20 and a suitable electrical connection 22 tothe electros luminescent field-voltage supply, described hereinafter. A foundation-viewing plate 24 is placedover one of the conducting layers, for example electrode layer 18 and an insulating klayer'26may be placed over the otherV conducting'electrodelayer16, Vin order-to minirrtizceshocl: hazard. A protecting and Yhandling shield 28 may be provided around the entire periphery vof the screen inLorlder to facilitate storage, handling', etc.

vTheA luminescent materialV layeif 12 Vis preferably positioned next to the foundation-viewing plate 24, 'although for some applications it 'maybe preferable to place the dielectric layer 14 next tothe viewing plate 24'. The thickness of thegluminescent material layer 12'is-not particularlycr'itical, but as a specitic example it vmay have a thickness'of 0.2 mm. 'The'dielectriclayer' 14 may comprise any suitable dielectric which has a high dielectric constant, is transmissive to either visible light or to X-rays depending upon its' position within the screen, and will not rapidly deteriorate under the action "outswitch-44, camera tilm 46, cameraQshutter-tripping of X-rays. SuchV materials larewell known" and as. anv

eiiample, the dielectric material layer'14 lmay comprise a' miea' sheet 'about 0.05 thick, although this thickness isin no way'critical'and may be increased or de'- creased as indicated by the application. Alternative constructionsare valso possible in the screen 10v and a suitable dielectric inmaterial vsuch as polyvinylchloride acetate *may* be admisedwith the phosphorand the yseparate dielectric'layer dispensed with, if desired, or the dielectric `material may be dispensed with entirely in some special applications and only the phosphor layer 12 placed between the electrodes 16 and 18. It should be pointed out that the purposeot the dielectric material is to prevent electrical breakdownl through the phosphor and between the `electrodes 1 6 and` 18 and the electric elds as may be used'hereinlneednot be particularly intense. VThe usableelectric fields, however, may vary over a wide range asin the heretofore-mentioned copendiug Destriau application and as a specific example, the `electric field which Vis'applied acrossthe screen may have an intensity of 2 0 lv. per cm.

kThe conducting electrodes 16 and 18 may be fabricated of any conducting materials which may be coated as a'thin sheet and aretransmissive to visible light in the case of the lower layer 18 and transmissive to X-rays in the case of the upper layer 16. 0f course these electrodes should not deteriorate appreciably under the action of X-rays. `As an example, the eiectrode 18 may be fabricated of a thin layer of tin oxide on a glass base, such assold under the trademark Nesa by Pittsburgh Plate Glass Co., Pittsburgh, Pa. Other suitable thin, conducting coatings such as oxides of zinc, cadmium, aluminum or bismuth, `for example, may also be used. The yelectrode 16 may be fabricated of tin oxide, for eirample, or it may bea thin coating of aluminum which may be applied bythe wellfknown vacuum-metaliz'ing techniques. The thinprotective layer 26, which is iutended to insure against shock hazard and to facilitate handling, maybe fabricated of any X-ray-transparent material which has relatively good electrical insulation properties and plastics such as polytetrauoroethylene are suitable. The protective layer26 may be dispensed with, if desiredand the shock hazard eliminated by grounding the electrode 16.y

The foundation-glass viewing plate may be fabricated of any glass which contains heavy atoms whichwill absorb the X-rays and thus protect the viewer or the photographic plate, as the case may be. As an example, any ofthe well-knownlead or cerium glass may be used. The protecting and handling shield 28 may lbe fabricated of a plastic similar to the layer 26 and this shield may be dispensed with, if desired.

In Fig. 2 is illustrated, in block diagram, one embodiment of a suitable X-ray apparatus which in this showingfis set to presensitize 'the fluoroscopic screen, as explained hereinafter. This' apparatus 30 comprises gener'- ally Aan X-ray rectifier-*and transformer uuitj32, X-ray' and film shutter timer 34,"Xray tubef 36, field-voltagecontrolv unit 38, field-timer'unit 40, the X-ray fluorounit 48 and camera shutter 50. All of the components -of this apparatus are well known with the exception of the X-ray-uoroscopic screen 10, which has been described in detail hereinbefore, and which screen may be identical, if desired, with the corresponding screen described in the heretofore-mentioned copending Destriau application. Also,'the` use of automatic timers may be eliminated, if desired, and the-entire timing sequency may be carried out by hand.

In Fig. 3 is shown in block diagram the samc'X-ray apparatus as shown in Fig. 2, but with thel electric field cutout switch 44 in an open position. With the X-ray tluoroscopic screen presensitized, the apparatus is'thus set to release either a stored image or a stored image which is also enhanced in luminous output. The details of the operation of this apparatus will be consideredin detail as thek description proceeds.

In Fig. 4 -isshown. a graph' ofl brightness in arbitrary unitsvs. time inl minutes illustrating Vthe vstorage eleet' of the X-ray-fiuoroscopic screen 10 Ywhen operatedin the prescribed manner. When X-'ra'ys are first passed th'r'oii'gh the object 52A to generate an `Xr`ay` signaLby closing the exposure switch 42 (with the field-control switch 44 in the down position) the brightest lresponse of the uo'ros'c'o'pic screen 1t) Vto theX-ray signal is represented by the line A-C-D. Upon application of the electric field across the` screen electrodes v16 and 18, as controlled by-the eld timer unit 40, the brightness of the image is greatly enhanced as per the line D-E in Fig. 4.l A momentary brightness peak isl realized upon application of the electric field, and thereafter the brightnessstabilizes at an enhanced value, as represented by the line F-G vin Fig. 4. This simultaneous screen excitation'hy an X-ray signal, while the screen'is `within the influence of an electric field, serves to presensiti'ze the-fiuoi'oscopic screen 10 and to eaiseit tostore the image, which stored Vimage can later be released, provided the. prescribed sequence of operations is followed. Of course, without the simultaneousN application of the electric eld across the phosphor screen, the brightness would follow the dotted, line D-D', as shown in Fig. 4.

The Xfray signal is preferably discontinued before the electric field is yremoved and this may be accomplished by theX-ray timer 34 which may beset to cut off the X-ray signal just before the field is cut ott. Immediately after cuttingl oif the X-'ray signal, such as ten Yseconds later for ve`xar'nple,'the electric field may be cut off by removing the 'potential' across the electrodes 16 and 18 and this may be aeeomplished by means of the A C. field timer 40. The Xiray-uoroscopic screen 10is then allowed torernainy quiescent until it is desired to 4repro'- duce the signal. In such areproduction, the object 52 being X-rayed is removed' from between the uoroscopic screen 10 aud the X-'ray tube 36 and the X-ray apparatus is set up to release the stored image, as illustrated in Fig. 3. Assume for example, that the period of delay between the screen prsensitization and the release of the stored image is two minutes. The object 52 being X-rayed is removed from the X- ray table during this interval and the field-control, double-throw switch 44 is elevated so as to render operablethe camera-shutter tripping unit 48. The X-ray-fluoroscopic screen 10 is then irradiated with substantially uniform intensity X-rays and the brightest part of the screen will lfollow the line I--I--K,A as shown in Fig. 4, as Vtheifriage is released. At point K, the stored image will be completely removed' and the screen will luminesce substantially evenly over its entire surface due to the substantially uniform X-ray irradiation. Inthe s 'pecii'ic example as shown in Fig. 4,' the intensity of the second' X-'ray irradiation utilized to cause the" stored image to release is the same asjthe maximum intensity of the X-rays which'were-used to effect the screen presensitization, but it is not necessary to use the sameA intensity X-r'ays, as willbe explained hereinafter.l Also, thestoredimage is shown as expending itself in about oneminute and this time may be varied considerably depending upon the equipment operation as explained hereinafter. Of course, if the screen 10 were not presensitized, the luminosity developed in the screen under the X-ray irradia-- tion would follow the dotted line IK, as shown in Fig. 4. The degree of presensitization of the-phosphor screen should not be excessive as the screen presensitization tends to saturate. At complete saturation, the contrast between portions ofthe memorized image will be lost and the degree of screen presensitization will be quite similar over the entire screen. For the specific zinc-cadmium sulfide, manganese-activated phosphor, presensitization saturation will be realized under X-ray irradiation which is equivalent to that effected by a total quantity (Q) of X-rays striking the screen of about 160 microampere-minutes (assuming no object between the tube 36 and the screen l0). Of course, when an object is to be X-rayed, a larger quantity-of X-rays may be used without saturating the screen presensitization since the object being X-rayed will absorb a considerable amount of the radiation. It is noted that screen presensitization is not effected by the field alone, nor will the electric field alone, as specified, develop an appreciable pure electroluminescence in the screen 10. The X-ray tube 36 as used herein had a hard glass window and was operated at a voltage of 80 kv. with a self-rectified circuit. The target material was tungsten and the distance from the centerline of the tube 36 to the screen 10 was about 20 cm. Under these conditions of operation, the tube current and time were measuredv to the indicated values of Q. Of course, these conditions of operation may be varied depending on the application. -In Fig. is illustrated the operation of the unit in order to achieve an enhanced luminosity for the stored image. As an example, the initial screen presensitization for the most X-ray-transmissive portions of the object, X-rayed may be effected by a total Q of 160 microampere-minutes. In operating the unit to produce the results as illustrated, the iield and the presensitizing X-rays are simultaneously applied and the resulting luminosity of the screen follows the curve L--M-N. Without simultaneous application of the eld, the screen luminous response to the X-ray irradiation alone would follow the dotted curve L-L'. At the end of two minutes of X- ray irradiation while under the simultaneous nliuence of an electric field, the X-ray excitation is removed and shortly thereafter the field is removed. The object being X-rayed is then removed from the X-ray table and the switch 44 is thrown to facilitate actuating the shutter-.- tripping unit 48. After closing the exposure switch 42,; the camera shutter 46 will be opened at the proper time as controlled by the shutter timer in timer unit 34. The X-ray-uoroscopic screen is then irradiated with relatively intense X-rays and this will release the stored image as a transient picture, the brightness of which will follow the solid line O-P-R. As an example, the timing unit 34 may be set to open the camera shutter 50 five seconds after the image-releasing X-ray irradiation is started, in order to photograph only the brightest portion of this transient reproduction ofthe stored image. In the specific example as shown, the substantially uniform intensity X-rays which have been used to release the stored image with an enhanced luminosity are approximately ten times as intense as the most intense screen-presensitizing irradiation. In explanation, the presensitizing X-ray intensity striking the screen portion adjacent the most X-ray-transparent portion of the object was equivalent to that effected by 80 microarnperes tube current with no object in place, s uch irradiation being for two minutes. The releasing X-ray irradiation, represented by the symbol (j) was equivalent to 800 microamperes tube current. Of course, an equivalent screen presensitization could be effected .6i by an X-ray current y of greater intensity applied' l fory a'- shorter period. I 'I g It should be noted that the screen presensitization is not dependent upon the intensity of the X-rays, but rather is dependent upon the total quantity of X-rays striking the screen,vnamely the intensity times the time. The intensity of the released picture normally is dependent upon the intensity of the releasing X-rays and the greater the intensity of the releasing X-rays, the greater the intensity of the released image and the more transient in nature it becomes. In the specified example shown in Fig. 4, the released image extends over a total period of about one minute and in the specic example shown in Fig. 5, the brightest portion of the released image extends only over a few seconds and it is necessary to record photographically such released image in order to analyze same. Under other conditions-of operation, however, where the X-ray intensityof the image-releasing irradiation is relatively 1ow, the released image may extend over two minutes or longer. In such operation, it may not be del `siirable to record photographically the released image.

. In Athe example given hereinbefore, the X-ray signal irradiation of the uoroscopic screen 10 has been stopped before the field has been removed and this is to insure that the screen will not be desensitized. It is possible, of course, to stop the X-ray irradiation and to remove the field simultaneously, and the removal of the field may even precede the X-ray signal irradiation provided that the time interval between the two is not too long. Such a procedure, however, will sacrifice some of the presensitization and if the period of time which the removal ofthe field exceeds the removal of the X-rays is 30 seconds or longer, for example, the presensitization of the phosphor Screen will generally be very small. The advantages of the process and system disclosed herein'are that a portion of a living organism can be X-rayecl by utilizing only relatively low-intensity X-rays to a total quantity striking the screen of micro. ampere-minutes, for example, to presensitize the screen.` The X-rayed object can the'nbe removed from the X-ray table and the vpresensitized screen irradiated with X-r'ays of considerably stronger intensity. This will produce a very bright reproduction of the stored image without exposing the object being X-rayed to the later-applied X-rays. In addition, the images of animate or inanimate objects may be stored in the presensitized screen for later observation.

In Fig. 6 'is illustrated'xa graph wherein the ratio of brightness of the released image (Bm) divided bythe brightness of an Aunsensitized screen under similar X-ray' irradiationfBo) is plotted vs. time in minutes and as illustrated, even with quiescent periods of up to about 17 hours, the stored image will. still retain considerable brightness when released. It vshould be notedthat irradiation of the presensitized iiuoroscopic screen with visible light or with ultraviolet will impair the presensitization and it is desirable to protect the presensitized screen from such unwanted radiations in order to protect the stored signal.

In the foregoing example, the quantity of X-rays expressed in microampere-minutes (Q) and the image releasing current (j) have been specified. It should be understood that the conditions of operation can be modified considerably if desired. Also, the X-ray image-releasing irradiation has been indicated as of uniform intensity. It should bel understood that non-uniform intensity X-rays could be used to effect the .release of the stored image, if graded intensities in the brightness of the released image were desired.

It should be clear that the equipment may be operated so as to emphasize certain X-ray transmissive portions of the object being X-rayed. For example, the initial X-ray irradiation of the screen may be of such intensity that' the presensitization of the screen will be saturated for all but the most X-ray-opaque portions of the-.ob-

a* egress `7 ictf' Being X-rayed `Uponl releasing 'the 'stored image, only these corresponding unsaturated portions 'of the screen will-display alcontrastd image, `which image may be observed or phtegraphed. Thus mty uestfea prtions of the object being X-'rayed may be emphasie'd.

It will be `recognized that the objects of the -inyenti'on have been achieved by providing amethod for storing and later releasing the luminous response to an -X-ray signal of an X-ray-responsive 'phosphor screen, which stored image may be released with enhanced output, if desired. In the instant method of operation, during the screen presensitization, the object being X-iayed is irradiated "to generate the screen-applied X-ray signal and the Yfield is simultaneously applied across the screen. The object and lield are then removed and uniform-intensity X-rays applied to the presensitized screen. -In copending applicasion of G. Destriau, the inventor herein, titled X-Ray Method, SN. 645,742, tiled concurrently herewithfand assigned tothepresent assignee,- is disclosedmethod for operatin'glthe same X-r'ay equipment 'as disclosed herein, but dite'ring in that the'obiect is twice-irradiated withX-rays '5to generate a signal on both the screen presensitization and the second screen X-ray-irradiation. The contrast in the resulting image can be varied by this method. In copending application of G. Destriau, the inventor herein, titled Method for Operating X-Ray Device, S.N. 645,695, filed concurrently herewith and assigned to the present assignee, is disclosed a method for operating the same X-ray equipment as disclosed herein, but differing in that the object is not between the X-ray tube and the screen when the screen is presensitized by uniform intensity X-rays and the applied field. The object is thenplaced between the tubeand the presensitized screen and the resulting X-ray' signal is applied to the screen. By this lmethod'a relatively-intense X-ray signal maybe applied to generate a correspondingly bright and transient image, without -overexposing the object to X-rays. In addition, the screen contrast may be varied. It'should be clear that the three methods basically differ by the presence or absence of the object being X-rayed during the screen presensitizationand the later X-'ray irradiation.

. While in accordance with the Vpatent statutes, one bestltnown embodiment of the invention has been illustrated and described in detail, it is to be particularly understood that `the invention is not limited thereto or thereby.

I claim:

l. The process of storing and later releasing the luminous response to an X-ray signal of an X-ray-responsive phosphor screen 'characterized by displaying an enhanced luminous output when excited by X-rays `and simultaneously placed within the inuence of an alternating electricfield, said process comprising passing X-rays of-preselected intensity through an object having varying per'- meability to X-rays to generate an X-ray signal, applying to said screen said X-ray signal and simultaneously applying across said screen an alternating electric field to effect a phosphor-screen presensitization varying in amount with the quantity of X-rays applied thereto and corresponding to said X-ray signal, removing from said presensitized screen said applied X-ray signal and said applied electric field, and thereafter irradiating saidv screen with X-rays, whereby a screen luminous image corresponding to the screen-applied X-ray signal is reproduced thereon.

2. Thek process of storing and later releasing the luminous response to anV X-rayl signal of-an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when excited by V15C-rays and simultaneously placed within the influence of an alternating electric field, said process comprising passing X-rays of preselected intensity through an object having varying permeability to X-rays `to generate an X-ray signal, applying to-`said lscreen- 'said X=ray signaland si- 'iauleneousty applying aero-ss 'said' sefen--an-altera'anag electric A field to effect. a phosphor-screen. presensitiiation 'venting Vin ernennt with un; quantity of 1c-rays apprise thereto and' cor'espond-ing to said X-ay signal,- removing said psensitied'sc'reen said applied X-rayi" signal and said applied elctictield, and thereafter irradiating' said screen with' substantially uniform intensity X-r'ays', whereby a screen luminous image corresponding to the screen-applied X-ay signal is reproduced thereon.

3. The process of storing and later releasing the -luminous response to an X-ray signal of an X-ray respon,- sive phosphor screen characterized by displaying an enhanced luminousv output when excited by X-rays 'and simultaneously placed within the influence of an alter-l nating f electric eld, said process comprising passing X-'ray's of preselected intensity through an object having varying permeability to X-rays to generate an X-ray signal, applying to said screen said X-ray signal and simultaneously applying across said screen an alternating electric field to effect a phosphor-screen presensitization varying in amount withthe quantity of X-rays applied thereto and corresponding to said X-ray signal, removing fromsaid presensitized screen said applied X-ray signal, thereafter removing said applied electric field, and thereafter'irradiatiing said scren with substantially uniform intensity X-rays, whereby a screen luminous image corresponding to the screen-applied X-'ray signal is reproduced thereon.

'4. The process of storing and later releasing thc luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when excited by X-rays and simultaneously placed within the inliuence of an alternating electric field, said process comprising passing X-rays of preselected intensity through an object having varying permeability to X-rays to generate an X-ray' signhapplying to said screen said X-ray signal andsimultaneously applying across said screen an alternating electric eld to eiect a phosphor-screen presensitization varying in amount with the `quantity of -X-rays applied thereto'and corresponding to said X-ray signal, substantially simultaneously removing-from said presensitized screen 'said applied X-ray sginal and said applied electrioeld, and thereafter irradiating said screen with substantially uniform intensity X-rays, whereby a screen luminous image corresponding to the screen-applied X-ray signal is reproduced thereon.

5. The process of storing land later releasing the luminous response to an X-ray signal of an X-ray-responsiye phosphor screen characterized by displaying an enhanced luminous output when excited by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising passing X-rays of preselected intensity through an object having varying permeability to X-rays to generate an X-ray signal, applying to said screen 'said X-ray signal and simultaneously applying across said screen an alternating electric eld to eiect a phosphor-screen presensitization varying in amount with the quantity of X-rays applied thereto and corresponding to said X-ray signal, removing from said presensitized screen said applied X-ray signal and said lapplied electric field, and thereafter irradiating said screen with X-rays to generate a transient screen luminous image corresponding to the screen-applied X-ray signal, and recording said transient screen luminous image, whereby a screen luminous image corresponding to the screen-applied X-ray signal is reproduced thereon.

y6'. The process of increasing the luminous responseto an X-ray signal of an X-ray-responsive phosphor screen cliracteizedby displaying an enhanced luminous output when excited by X-rays and simultaneously placed Within the inuence of an alternating electric field, said process vcomprising passing X-rays of preselected intensity through an object having varying permeability to X-rays to generate 'an X-ray signal, applying to said screenlsaid X-'ray signal and-simultaneously applying across said screen-:an alternating electric field to effect a phosphor-Screenprosensitization vyingfinaniount 'with the quantity Vof X-rays aplied thereto and corresponding to said X-ray signal, removing from said presensitized screen said applied X-ray signal and said applied electric eld, and thereafter irradiating said screen with X-rays having substantially greater intensity than the intensity of said X-ray signal whereby a screen luminous image corresponding to the screen-applied X-ray signal is reproduced thereon.

7. The process of storing and later releasing with enhanced output the luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when excited by X-rays and simultaneously placed within the inuence of an alternating electric eld, said process comprising passing X-rays of preselected intensity through an object having varying permeability to X-rays to generate an X-ray signal, applying to said screen said X-ray signal and simultaneously applying across said screen an alternating electric ield to effect a phosphor-screen presensitization varying in amount with the quantity of X-rays applied thereto and corresponding to said X-ray signal, removing from said presensitized screen said applied X-ray signal, thereafter removing said applied electric f ield, and irradiating said screen with substantially uniform intensity X-rays having substantially greater in` tensity than the intensity of said X-ray signal, whereby a screen luminous image corresponding to the screenapplied X-ray signal is reproduced thereon.

8. The process of increasing the luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when excited by X-rays and simultaneously placed within the inuence of an alternating electric eld, said process comprising passing X-rays of preselected intensity through an object having varying permeability to X-rays to generate an X-ray signal, applying to said screen said X-ray signal and simultaneously applying across said screen an alternating electric eld to effect a phosphor-screen presensitization varying in amount with the quantity of X-rays applied `thereto and corresponding to said X-ray signal, substantially simultaneously removing from said presensitized screen said applied X-ray signal and said applied electric eld, and thereafter irradiating said screen with substantially uniform intensity X-rays having substantially greater intensity than the intensity of said X-ray signal, whereby a screen luminous image corresponding to the screen-applied X-ray signal is reproduced thereon.

9. The process of increasing the luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when excited by X-rays and simultaneously placed within the influence of an alternating electric eld, said process comprising passing X-rays of preselected intensity through an object having varying permeability to X-rays to generate an X-ray signal, applying to said screen said X-ray signal and simultaneously applying across said screen an alternating electric ield to effect a phosphor-screen presensitization varying in amount with the quantity of X-rays applied thereto and corresponding to said X-ray signal, removing from said presensitized screen said applied X-ray signal and said applied electric field, and thereafter irradiating said screen with X-rays having substantially greater intensity than the intensity of said X-ray signal, to generate a transient screen luminous image corresponding to the screen-applied X-ray signal, and recording said transient screen luminous image.

References Cited in the le of this patent Electroluminescence and Related Topics, Destriau and Ivey, Proceedings of IRE, December 1955, pp. 1911 to 1937. 

